1. Field of the Disclosure
Embodiments of the present invention relate to an antenna checking circuit that is built in a communication device, to which an antenna is connected, and that checks the connection state of the antenna.
2. Description of the Related Art
In a communication device that is used in a wireless local area network (LAN) system or the like that is installed in a vehicle or the like, it is important that an antenna is properly connected to the communication device in order to transmit and receive radio waves in an optimal way. An antenna checking circuit that checks whether the connection state of an antenna is normal may sometimes be incorporated in such a communication device.
FIG. 5 illustrates an example of such a communication device of the related art. A wireless communication device 900 described in Japanese Unexamined Patent Application Publication No. 2010-010841 is a wireless communication device in which an antenna 910, which has a power supplying point connected to a terminal 912 and receives incoming radio waves, and a receiver 930 are connected by a signal line 952. The wireless communication device 900 includes a signal analysis unit 932 that includes direct-current (DC) signal applying means configured to apply a DC signal to the signal line 952 via an internal resistance 942. During operation of the DC signal applying means, whether breaking of the signal line 952 or a connection failure has occurred is checked by determining whether the voltage at one end of the internal resistance 942 on the side opposite to the side on which the DC signal applying means is disposed, that is, the voltage at an output terminal 943, is equal to or greater than a threshold. Since the wireless communication device 900 is configured as described above, breaking of the signal line 952 and a connection failure of the antenna 910 can be appropriately checked.
However, in the wireless communication device 900, an antenna that does not have a ground point is assumed to be used as the antenna 910, which is connected to the terminal 912, and in the case where an antenna that has a ground point and whose DC impedance between a power supplying point and the ground point is 0Ω, for example, an inverted F-shaped antenna, is connected to the terminal 912, the connection state of such an antenna cannot be precisely checked.
These and other drawbacks exits.